Gas Fired Heating Device and a Method of Generating a Flow of Hot Air

ABSTRACT

The invention relates to an apparatus for the heating of roofing material. The apparatus comprising: air supply means ( 86 ); an elongated tubular combustion chamber ( 10 ) with a first end ( 11 ) and a second end and having a wall ( 30 ) surrounding a longitudinal axis (A) of said combustion chamber ( 10 ) and including an exit for hot air at said second end ( 12 ) and at least one air entrance ( 50 ) near said first end ( 11 ) for delivery of a primary air flow. A burner arrangement is disposed essentially centrally within said combustion chamber near said first end. The burner arrangement comprises means for injection of fuel ( 88 ) and means for ignition of said fuel ( 80 ). The first end ( 11 ) of the combustion chamber being essentially air-tight, and said at least one air entrance ( 50 ) being located in the wall ( 30 ) of the combustion chamber ( 10 ) near said first end ( 11 ). The air entrance ( 50 ) comprises means to produce a helical current of air around said longitudinal axis (A) of the combustion chamber ( 10 ). The invention also relates to a method of generating a flow of hot gases in an apparatus for heating of roofing material

The invention relates to an apparatus for the heating of a bituminousroofing material, the apparatus comprising: air supply means; anelongated tubular combustion chamber with a first end and a second endhaving a wall surrounding a longitudinal axis of said chamber andincluding an exit for hot air at said second end and at least one airentrance near said first end for delivery of a primary air flow and aburner arrangement disposed essentially centrally within said combustionchamber near said first end, said burner arrangement comprising meansfor injection of fuel and means for ignition of said fuel.

Many heating devices for domestic and industrial use require a heatsource. When applying a bituminous roofing material on a roof, torchesare directed at the bitumen layer of the material in order to make thislayer soft and sticky so that the material will adhere to the surface tobe covered. It is well known that torches producing a flame or a hot airstream for welding or other purposes may be the cause of injuries topersons or fires if a person or structure is exposed to the flame for aperiod of time.

The provision of air chambers surrounding burner nozzles has beensuggested to overcome this problem. For example, U.S. Pat. No. 3,883,290discloses a burner where the generated stream of hot air is surroundedby an air current which insulates the wall of the guide pipe againstheating.

This device has a substantial disadvantage. Extensive heat is stilldeveloped in the area proximate to the ignition and burner arrangement.Therefore the burner and ignition arrangement has to be constructed frommaterials which are able to withstand these temperatures. Furthermore,no known material will last indefinitely if heated, and the expensiveceramic materials used in prior art apparatus are subject to thermalshocks and will therefore deteriorate thereby limiting the longevity ofthe system.

The object of the invention is to solve the problem of high temperaturesin the area proximate to the ignition and burner arrangement in aheating apparatus.

The object of the invention is achieved by a heating apparatus providedwith a first end being essentially air-tight and said at least one airentrance being located in the wall of the combustion chamber near saidfirst end, the air entrance comprising means to produce a helicalcurrent of air around said longitudinal axis of the combustion chamber.The supply of air leaves the centre axis of the combustion chamber moreor less unaffected by the surrounding helical current of air. Thisentails a relatively calm and rich burning of fuel along the centre axisof the combustion chamber. The centrifugal forces caused by the incomingair affect the cooler air stream with a higher density to the effectthat it is thrown against the wall of the combustion chamber and coolsit, while the hotter gas stream, with a lower density, is gathering inthe core zone.

According to a preferred embodiment, the at least one air entrancecomprises an angled scoop, an angled hole or an angled tube.

According to a preferred embodiment, said burner arrangement comprisesfuel injecting means adapted to inject the fuel in a directionessentially concentrically with said longitudinal axis (A) of thecombustion chamber (10).

According to another preferred embodiment, the burner arrangement haswall means adapted to fit said apparatus to make said combustion chamberair-tight at said first end. Preferable the burner arrangement isreleasably connected to the combustion chamber. This will facilitateaccess to the apparatus interior and thereby allow overall maintenanceas well as easy renewal or replacement of worn parts.

According to another preferred embodiment, the location of the airentrance is at or downstream of the means for injection of fuel. Thiswill make the initial gas air mixture richer in gas and therefore itfacilitates the ignition.

The air entrance may preferably be at or downstream of both said meansfor injection of fuel and said means for ignition of said fuel.

A further object of this invention is to provide a heating apparatuswith improved heating effects and a flame-free stream of hot air havinga great uniformity in the temperature profile at the outlet.

This object of the invention is achieved by the apparatus furthercomprising means for introducing a secondary helical current of air, thesecondary current of air having a direction of rotation opposite thedirection of rotation for the primary air and being introduced furtherdownstream the combustion chamber. The counter-flowing enteringsecondary air not only retards the helical motion and centrifugaleffect, but it also slows down the formation of any excessive greataxial velocity in the area of the core zone. The result is a flame-freestream of hot gases with a great uniformity in the diametric temperatureprofile at the outlet. The air entrance for said, at least one secondaryairflow, can preferably be made as an angled scoop; angled hole or as anangled tube.

In a preferred embodiment, the apparatus comprises a mixing chamberarranged in extension of said combustion chamber at said second end inwhich chamber the mixing of the counter-flowing currents of primary andsecondary airflows takes place. This improves a better mixing of primaryand secondary airflows.

In a further preferred embodiment, the mixing chamber arranged inextension of said combustion chamber and the apparatus are releasablyconnected. By arranging the mixing chamber in extension of saidcombustion chamber and the apparatus being releasably connected, it ispossible both to remove said mixing chamber for maintenance purposes andto change between different mixing chamber units which are made suchthat they are suitable for particular tasks.

The apparatus may include a generally tubular housing surrounding saidcombustion chamber. This protects the operator against being charred orburned.

According to a preferred embodiment, the housing is arranged at leastpartially spaced from the combustion chamber thereby defining an air gapfor delivering secondary air, whereby the housing is maintainedrelatively cool during the operation of the apparatus.

In a preferred embodiment the helical motion of the secondary air isaccomplished by a helical spiral placed in the air gap bounded by theinside of the tubular housing and the outside of the combustion chamber.Preferably the air gap near said first end of the combustion chamberconstitutes the initial air path for both primary and secondaryairflows, said air path being subdivided into two separate air paths.This provides a more compact apparatus.

The invention in other aspect provides methods as recited in claim16-17.

The methods facilitate the practical applications of generating flow ofhot gases by way of providing both a relatively cool ignition area and amore efficient ignition inside the combustion chamber.

The methods further facilitate the practical applications of generatingflow of hot gases showing a great uniformity in temperature profile.

Further objects and advantages and features of the invention appear fromthe following description of the preferred embodiments given withreference to the drawings wherein:

FIG. 1 shows a heating apparatus assembly in a side view;

FIG. 2 a shows the inner barrier with a fixed helical element;

FIG. 2 b is a drawing in perspective of the inner barrier, viewed fromthe entrance, with a fixed helical element;

FIG. 2 c is a drawing in perspective of the inner barrier, viewed fromthe exit, with fixed a helical element;

FIG. 3 a shows the inner barrier with a fixed helical element, the inletports having closed sides;

FIG. 3 b is a drawing in perspective of the inner barrier, viewed fromthe entrance, with a fixed helical element, the inlet ports havingclosed sides;

FIG. 3 c is a drawing in perspective of the inner barrier, viewed fromthe exit, with fixed a helical element, the inlet ports having closedsides;

FIGS. 4 a-4 b is a detailed view of a preferred embodiment of the inletports and

FIG. 5 shows, in perspective, a preferred embodiment of the inlet portstaken along line b-b in FIG. 1.

All figures are schematic and not necessarily to scale and show onlyitems essential to the understanding of the invention, whereas otherparts have been deleted for the sake of clarity. Throughout the figuresthe same references are used for identical or similar means.

The hand-held burner shown in FIG. 1 comprises like prior artapparatuses, a combustion chamber 10 with a burner arrangement disposedmainly centrally therein and connected with a fuel supply 83, anignition arrangement 80 for the fuel and an air delivery system. The airdelivery system delivers a helical spinning airflow. However, instead ofusing an axial blower disposed behind the burner to deliver a helicalspinning airflow, the helical motion of air is accomplished by theprovision of one or more air inlets 50 positioned in the wall 30 of thecombustion chamber 10. These air inlets 50 preferably made as scoops, asbest seen in FIG. 2-3, introduce into the combustion chamber 10 aprimary airflow in a direction essentially tangentially to the wall 30of the combustion chamber 10. The tangentially direction entails a flowof primary air through the combustion chamber 10 in a helicallycirculating motion around the combustion chamber's 10 longitudinal axisA. The circulating motion of primary air leaves the centre axis A of thecombustion chamber 10 more or less unaffected and thereby it facilitatesa rich current of fuel and gas along the axis.

As will be well known to those having operating experience with gasfired equipment, ignition is generally not possible in a lean mixture ofgas and air. To ensure an easy and safe ignition of the heatingapparatus, fuel is injected through the holes 88 in the burnerarrangement. The injection of fuel gives rise to a relatively calm andrich current of fuel and air along the center axis of the burningchamber 10 and thus it facilitates an easy and safe ignition. The fuelis preferably injected in a direction parallel to and concentricallywith the centre axis A of the combustion chamber 10.

As more clearly seen in FIGS. 2 a-3 a, the inlet 50 could be made asangled scoops, and said scoops could be made with open sides as bestseen in FIGS. 2 a-2 c or with closed sides as best seen in FIGS. 3 a-3c. As an alternative to scoops, the inlet ports could be made as angledholes or angled tubes as seen, in cross sectional view, in FIGS. 4 a and4 b. However, the helical current may be obtained in many other ways.

The ignition device comprises two electrical terminals 81 and 82 wherethe first terminal 81 is grounded, but any conventional ignition meanscould be used, e.g. a spark plug. After ignition of the fuel gasmixture, the initially still cold mixture of fuel and air travelsthrough the combustion chamber 10 in a helical rotation about thecombustion chamber's 10 longitudinal axis A. Due to the centrifugalcaused thereby, the relatively cooler airstreams (with the highestdensity) are thrown against the wall 30 of the combustion chamber 10,while the hotter airstreams (with a lower density) are concentrating inthe core zone along axis A. This entails a cool ignition area, and thebracket 85, which serves as a holder for the gas distributor 84 and theterminal 82 can therefore be made of materials which do not necessarilyhave to be able to withstand the high temperatures normally prevailingin the area proximate to the ignition. An especially inexpensive burneris achieved when the bracket 85 is made of an electricallynon-conducting material such as plastic, but other electricallyinsulating materials could be used.

Preferably the bracket 85 is adapted to make an air-tight fit againstthe wall of the combustion chamber 10 so as to seal the rear end of thecombustion chamber 10. The bracket 85 is releasably fastened by a nut87.

The hot air leaves the combustion chamber 10 in the form of a spinningcurrent. Such a spinning current has a density which increases from theaxis outward as a result of the centrifugal forces. In the area of thelongitudinal axis A the density of air is very low and the temperaturecorrespondingly high. Therefore the diametric temperature profile of thespinning current of hot air leaving the combustion chamber 10 does notshow a great uniformity. To slow down the helical motion of the hot airleaving the combustion chamber and thereby improve the temperatureprofile of the leaving hot air, the apparatus comprises in a preferredembodiment means for introducing a secondary helical current of air. Thesecondary current of air is introduced is with a direction of rotationopposite the direction of rotation of the primary air and is introducedfurther downstream the combustion chamber.

To maintain a cool exterior, the combustion chamber 10 is preferablymounted inside an outer housing 40 which is cooled by air deliveredthrough the air gap 41 between the outer housing 40 and the combustionchamber 10. Advantageously the air gap 41 constitutes a part of the airpath for both primary and secondary air supplied by a single air supplysystem through an initial channel 86. The inlets 50, which arepositioned in the air gap 41 and just downstream of the electricalterminal 81 serve as entries for the primary air into the combustionchamber 10, and a helical spiral 60 positioned further downstream setsup a counter-flowing helical motion of the secondary air.

In some particular cases it is advantageous to modify the inclination orlength of the helical spiral 60 to alter the overall air resistance ofthe secondary air supply. By changing for instance the inclinationand/or length of the helical spiral 60 both the speed and/or angle ofentry of the secondary air may be varied. But it is also possible toadjust and adapt the flow path of the primary and secondary air suchthat a single air supplier initially feeds all air through one singleinitial channel 86 which is downstream subdivided into two separatepaths for primary and secondary air currents.

The majority or all of the mixing between the counter flowing primaryand secondary air preferably takes place in a mixing chamber 20 arrangedat a foremost 12 second end of the combustion chamber 30.

To facilitate maintenance of the apparatus, the combustion chamber 10and the mixing chamber 20 are releasably connected by joints 22, e.g.snap-on mechanisms. By modifying the mixing chambers parameters, forinstance the outlet profile 21, the length of the mixing chamber, thediameter of the mixing chamber or the ratio between these parameters, itis possible to design special mixing chambers suitable for particulartasks, and the joints 22, make it possible to select and mount themixing chamber most suited for the actual task.

Although specific embodiments have been described above it is emphasizedthat the invention may be exercised in several ways and that theexplanation given above serves exclusively to clarify the invention andnot to limit the scope of protection conferred, which is definedexclusively by the appended claims.

Although the invention has been discussed in relation to bituminousroofing material, the apparatus may be used for applying a bituminousweb of any type of civil engineering structure.

1. An apparatus for the heating of roofing material, the apparatuscomprising: air supply means an elongated tubular combustion chamberwith a first end and a second end and having a wall surrounding alongitudinal axis of said combustion chamber and including an exit forhot air at said second end and at least one air entrance near said firstend for delivery of a primary air flow; a burner arrangement disposedessentially centrally within said combustion chamber near said firstend, said burner arrangement comprising means for injection of fuel andmeans for ignition of said fuel; said first end being essentiallyair-tight, and said at least one air entrance being located in the wallof the combustion chamber near said first end, the air entrancecomprising means to produce a helical current of air around saidlongitudinal axis of the combustion chamber. wherein the apparatuscomprises a means for introducing a secondary helical current of air,the secondary current of air having a direction of rotation opposite thedirection of rotation for the primary air and being introduced furtherdownstream the combustion chamber.
 2. Apparatus according to claim 1,wherein said at least one air entrance comprises an angled scoop, anangled hole or an angled tube.
 3. Apparatus according to claim 1 whereinsaid burner arrangement comprises a fuel-injecting means adapted toinject the fuel in a direction essentially concentrically with saidlongitudinal axis of the combustion chamber.
 4. Apparatus according toclaim 1, wherein said burner arrangement has a wall means adapted to fitsaid apparatus to make said combustion chamber air-tight at said firstend.
 5. Apparatus according to claim 4, wherein said burner arrangementis releasably connected to the combustion chamber.
 6. Apparatusaccording to claim 1, wherein the location of the air entrance is at ordownstream of said means for injection of fuel.
 7. Apparatus accordingto claim 1, wherein the location of the air entrance is at or downstreamof both said means for injection of fuel and said means for ignition ofsaid fuel.
 8. Apparatus according to claim 1, wherein by the means tointroduce the secondary helical current of air comprises at least oneangled scoop; an angled hole or an angled tube.
 9. Apparatus accordingto claim 8 wherein the apparatus comprises a mixing chamber arranged inextension of said combustion chamber at said second end, in which mixingchamber the mixing of the currents of primary and secondary airflowstakes place.
 10. Apparatus according to claim 9, wherein the apparatusand the chamber arranged in extension of said combustion chamber arereleasably connected.
 11. Apparatus according to claim 1, wherein agenerally tubular housing surrounding said combustion chamber isincluded.
 12. Apparatus according to claim 11, wherein said combustionchamber and said housing are arranged at least partially in spacedapart, thereby defining an air gap for delivering said secondary air tosaid chamber, whereby said housing is maintained relatively cool duringthe operation of said apparatus.
 13. Apparatus according to claim 12,wherein a helical spiral placed in said air gap and bounded by theinside of the tubular housing and the outside of the combustion chambergenerates the helical motion of the secondary air.
 14. Apparatusaccording to claim 13, wherein the air gap near said first end of thecombustion chamber constitutes the initial air path for both primary andsecondary airflows, said air path being subdivided into two separate airpaths for primary and secondary air.
 15. A method of generating a flowof hot gases in an apparatus for heating of roofing material, saidmethod comprising: feeding a flow of combustible gas into a combustionchamber; delivering a primary airflow in a direction essentiallytangentially to the longitudinal axis of said combustion chamber;directing a discharge end of said combustion chamber towards saidroofing material; igniting the mixture of gas and air inside thecombustion chamber; ejecting a flow of hot gases from said combustionchamber; feeding a secondary airflow downstream of the entry of primaryair, the secondary airflow having a direction of rotation opposite thedirection of rotation for the primary airflow.